I don't know specifically about the G1X macro suitability for your task but I can tell you about some pitfalls that I have experienced with other G- and S- cameras (and DSLRs) for this application. I have found that the "macro" modes and/or close-up lenses (think only of 2-element achromats - they are far superior) allow excellent closeups of bugs etc. BUT...... the problem for slide duplication is called field curvature and means that you can decide between getting the centre or the edges of your photo in focus. No problem for bugs etc. but for slides or coins etc. it is a problem. Stopping down reduces it, but somewhere around f/11 (for the G1X) you start getting diffraction softness. Distortion can also be obvious, depending on the system used.

Yes, there is a reason why macro lenses of many hundreds of $ are bought and used for closeups in preference to much cheaper solutions.

You will have to try out your closeup lens on the G1X to see how the result is.

I am considering the purchase of a G1X, so I would be interested in your findings. Please post.